#include <iostream>
#include <string>
using namespace std;
class Fish{
    public:
        virtual  void Swim(){
            cout<<"fish swim"<<endl;
        }
};

class Tuna:public Fish{
    public:
        void Swim(){
            cout<<"tuna swim"<<endl;
        }
};

void UsingFish(Fish& fish){
    fish.Swim();
}

int main(){
    Tuna tuna;
    tuna.Swim();
    UsingFish(tuna);
    return 0;
}
